1. Field of the Invention
An aspect of the present invention relates to an image forming apparatus and a method of preventing a carrier from adhering to a photo receptor.
2. Description of the Related Art
In general, an image forming apparatus prints a desired image by forming an electrostatic latent image on a photosensitive medium using an exposure unit, such as a laser scanning unit, in response to a digital image signal, developing a toner image by supplying a toner to the electrostatic latent image, transferring the toner image onto a print medium, and fixing the toner image on the print medium by applying heat and pressure to the toner image.
Image forming apparatuses are classified into a dry type and a wet type according to a state of a toner and carrier generally used. The wet-type dry image forming apparatuses are also classified into two types: an apparatus having a one-phase developing device, and an apparatus having a two-phase developing device.
The one-phase developing device forms an image by supplying only a toner to the electrostatic latent image, while the two-phase developing device forms an image by supplying a carrier mixed with toner particles to the electrostatic latent image.
With regard to the one-phase developing device, after the toner is applied onto a photosensitive medium to develop a toner image, the toner left on a surface of the photosensitive medium is removed by a cleaning blade, and is recovered by a recovery unit to recycle the toner.
With regard to the two-phase developing device, after toner particles are supplied onto the photosensitive medium to develop the toner image, the toner particles left on a surface of the photosensitive medium are removed by a cleaning blade, and recovered by a recovery unit to recycle the toner.
However, in the two-phase developing device, when the cleaning blade removes the particles, adhesion of the carrier onto the photosensitive medium wears out the surface of the photosensitive medium, thereby grading down the performance of the photosensitive medium. Even though the carrier is removed from the surface of the photosensitive medium by the cleaning blade, the carrier abrades the cleaning blade. Therefore, the carrier preferably should not be adhered to the surface of the photosensitive medium.
A conventional image forming apparatus generally includes a photosensitive medium and a developing device. Also, the conventional image forming apparatus includes a charger for charging the photosensitive medium to a predetermined potential, and an eraser for removing the potential charged on the photosensitive medium, both of which are disposed around the photosensitive medium. The developing device has a developing roller for supplying the toner onto the electrostatic latent image formed on the photosensitive medium to develop the latent image as the toner image, and a mixing roller for homogenously mixing the toner with the carrier to prevent mixed particles from curing.
The developing roller and the mixing roller are connected to and driven by a main motor rotating the photosensitive medium. Hence, the developing roller and the mixing roller do not operate when the main motor is turned off. Also, when the main motor is turned off, the charger and eraser are also turned off. In other words, when the main motor is turned off, the developing roller, the mixing roller, the charger, and the eraser are all consequently turned off.
However, when the main motor is turned off, the photosensitive medium still rotates for a dwell period of time due to an inertial force. At this time, the charger and the eraser are also turned off, so that the potential required for development is cut off. The carrier is adhered to the surface of the photosensitive medium due to potential difference.
Examples of a method of preventing the carrier from adhering to the surface of the photosensitive medium which rotates after the main motor is turned off are disclosed in U.S. Pat. No. 6,212,339 entitled “Image Forming Apparatus with Discharging Exposure after Shutdown,” issued to Inoue, et al., on Apr. 3, 2001, and U.S. Pat. No. 6,070,032 entitled “Electrostatic Printing Apparatus Having an Erase Lamp,” issued to Rokutanda, et al., on May 30, 2000.
However, the above methods are complicated, and accordingly a method of easily and effectively preventing the carrier from adhering to the surface of the photosensitive medium is required.